Brass alloy

ABSTRACT

A brass alloy comprising (a) bismuth in an amount in the range from  0.5 - 1 % by weight, (b) lead present in an amount in the range of  0.15 - 0.25 % by, (c) tin present in an amount in the range of  0.25 - 1 % by weight, (d) a dezincification agent(s) present in an amount in the range of  0.02 - 0.4 % by weight, (e) copper present in the range of  60 - 63 % by weight, and (I) the remainder of the composition being essentially zinc.

FIELD OF THE INVENTION

The invention relates to a brass alloy. In particular, the invention relates to a brass alloy having a low lead content.

BACKGROUND OF THE INVENTION

In this specification, where a document, act or item of knowledge is referred to or discussed, this reference or discussion is not an admission that the document, act or item of knowledge or any combination thereof was at the priority date, publicly available, known to the public, part of common general knowledge; or known to be relevant to an attempt to solve any problem with which this specification is concerned.

The word ‘comprising’ and forms of the word ‘comprising’ as used in this description and in the claims does not limit the invention claimed to exclude any variants or additions.

Brass is an alloy of copper and zinc in which the proportions of copper and zinc and other elements can be varied to create a range of brasses. Brasses also frequently contain lead to improve machinability or to act as a lubricant. When lead is added to brass, the lead, which is nearly insoluble in brass, becomes discrete particles distributed fairly evenly throughout the brass. Then, when the brass is machined to form a component the surplus brass is removed in chip form rather than as long coils when no lead is added. This allows more complex parts to be machined with much easier removal of the surplus material from the tooling and the machine and with significantly less power being required for the machining process.

There is a worldwide trend for materials that are in contact with potable water to be restricted in composition so that the leaching of many of the contained elements into water is strictly limited. In many countries, including Australia and the USA, the amount of lead that is leached is measured under test conditions due to the risks to human health and the environment. In the State of California, USA, the amount of lead in the actual material will be limited by legislation effective 1, Jan. 2010 to 0.25% of the total composition. The legislation includes an averaging clause when a product contains several components some of which do not contain lead. For example, most taps (called faucets in some countries) and items such as mixing valves, water meters and pressure reduction valves, contain components that are made from plastics or metals that do not contain lead.

Accordingly, attempts are being made world wide to develop a cost effective brass alloy that contains either no lead or lead at less than 0.25% concentration that will comply with the new requirements in California.

However, it is not straightforward to eliminate lead from a brass alloy because the inclusion of lead is the most cost effective method of ensuring that the material has acceptable machining properties. Accordingly, any low-lead alloy will still need to have acceptable machining properties.

One attempt to achieve a low-lead copper alloy involves replacing some or all of the lead with silicon. One example of a silicon copper alloy which is claimed to have industrially satisfactory properties contains 69 to 80% copper, 1.8 to 4% silicon, 0.02 to 0.4% lead with the remainder consisting of zinc (U.S. Pat. No. 7,056,396). This silicon alloy may also contain small amounts of arsenic, antimony, aluminium, phosphorus, bismuth, tellurium and/or selenium depending on the desired final properties of the alloy.

Another attempt to achieve a low-lead or essentially lead free copper alloy involves replacing some or all of the lead content with bismuth. Bismuth has several properties that are similar to lead and, in particular, is also nearly insoluble in an alloy of copper and zinc. Therefore, bismuth aids machinability in a similar way to lead. One example of an essentially lead free copper alloy contains 1.8 to 5% by weight of bismuth (U.S. Pat. No. 5,137,658). Another example of a lead free wrought copper alloy contains at least 60% copper, at least 0.5% bismuth and at least one of phosphorus, indium or tin (U.S. Pat. No. 5,167,726). Bronze is a different copper alloy to brass but the use of bismuth to replace lead is also disclosed with amounts of 0.5 to 6% by weight of bismuth (U.S. Pat. No. 6,419,766).

However, whilst these resultant alloys containing bismuth may have acceptable properties, the resultant alloy has an increased cost because bismuth is now a very expensive material (significantly more expensive than lead). Another reason why bismuth has not been use extensively is that even small concentrations of bismuth in pure copper causes the copper to become brittle. In addition, bismuth may have toxicological ramifications for humans and the environment thus it would seem preferable to minimise the use of this element in alloys in contact with potable water.

There remains a need for a low lead brass alloy which is economic and meets the needs to reduce lead.

SUMMARY OF THE INVENTION

It has been found that a low-lead brass alloy can be produced that has the required five essential properties of good casting properties, good hot working properties, good cold working properties, good machining properties, good dezincification properties and also be less costly to produce than other low lead alloys so far developed. In particular, it has been found that the use of a small amount of lead in combination with bismuth, tin and a dezincification agent (eg arsenic, phosphorus and antimony) can produce a low lead brass alloy which has all five essential properties set out above.

According to the invention, there is provided a brass alloy comprising:

-   -   (a) bismuth in an amount in the range from 0.5-1% by weight,     -   (b) lead present in an amount in the range of 0.15-0.25% by,     -   (c) tin present in an amount in the range of 0.25-1% by weight,     -   (d) a dezincification agent(s) present in a total amount in the         range of 0.02-0.4% by weight,     -   (e) copper present in the range of 60-63% by weight, and     -   (f) the remainder of the composition being essentially zinc.

Preferably, the amount of bismuth is about 0.7% by weight.

Preferably, the amount of lead is about 0.22% by weight.

Preferably, the amount of tin is about 0.3% by weight.

Preferably, the dezincification agent(s) is/are selected from arsenic. phosphorous, antimony and/or any other dezincification agent. In one aspect, the dezincification agents(s) is/are preferable present in an amount of 0.02 to 0.3%. In another aspect the dezincification agent(s) is/are preferable present in an amount of 0.05 to 0.4%. In yet another aspect the dezincification agent(s) is/are preferable present in an amount of 0.05 to 0.2%.

Typically, the total amount of dezincification agent(s) is present in an amount of about 0.12% by weight. Preferably the dezincification agent(s) is arsenic and/or phosphorus.

Typically, single dezincification agents are used but the use of mixtures of these agents is not excluded from the scope of the invention. For instance, phosphorous is often used when arsenic is either not acceptable or only acceptable in quantities insufficient to achieve the desired dezincification properties. Accordingly, it is envisaged that in such a situation a combination of arsenic and phosphorous in the alloy may be adopted.

In essence, it has been surprisingly found that the presence of tin is more compatible with lead and bismuth than other elements e.g. aluminium and, in the above formulation, the proportions of lead, bismuth and tin have resulted in enhanced machining properties without adversely affecting the other properties. It is believed that it is the proportions of tin, lead, bismuth (and the presence of a dezincification agent) within the defined fairly narrow range that is important in this brass alloy in achieving the required five essential properties of good casting properties, good hot working properties, good cold working properties, good machining properties, good dezincification properties and also be less costly to produce than other low lead alloys so far developed.

Other elements, commonly referred to as impurities, may be present in each of the aspects and if present, no individual other element will be present in an amount of more than 0.2% by weight.

The person skilled in the art will understand that the ideal alloy will have as little lead and bismuth as possible given the potential application discussed whilst still retaining the desired acceptable machining properties. Preferably, the amount of bismuth present is about 0.7% by weight.

In practice, for brass alloys used in plumbing components, the zinc content is controlled by the need to comply with the Dezincification Requirements. Dezincification can be a problem in alloys containing more than 15% zinc. Dezincification selectively removes zinc from the alloy leaving behind copper rich porous structure that has significantly lower mechanical strength. The dezincification can progress through the brass weakening the entire component and causing it to leak.

As indicated the alloy of the invention contains a dezincification agent(s) to provide the Dezincification Resistant properties that virtually all copper based products in contact with water now need to have.

The brass alloy according to the invention can be produced using any known method. It can be produced using all new raw materials, or it can be produced using recycled alloy materials. or it can be produced using a combination of new and recycled materials.

EXAMPLES

Various embodiments/aspects of the invention will now be described with reference to the following non-limiting examples.

Example 1

This example demonstrates a brass alloy according to the invention.

A brass alloy was prepared having the following composition limits:

Component Amounts (% weight) Bismuth 0.69 Lead 0.21 Tin 0.26 Arsenic 0.08 Zinc 37.6 Copper 61.1 Other elements Max any one element 0.2%

The alloy was prepared using 70/30 copper/zinc alloy (purely copper and zinc with low impurities), 60/40 lead bearing brass scrap, bismuth, tin and copper arsenic alloy.

Example 2

This example provides another example of he alloy according to the invention.

A brass alloy was prepared having the following composition:

Component Amounts (% weight) Bismuth 0.72 Lead 0.23 Tin 0.34 Arsenic 0.13 Zinc 36.8 Copper 61.7 Other elements Max any one element 0.2%

The alloy was prepared using 70/30 copper/zinc alloy (purely copper and zinc with low impurities), pure bismuth, 60/40 lead bearing brass scrap, bismuth, tin, and copper arsenic alloy.

Results

The resultant alloys of Example 1 and Example 2 were found to have the required five essential properties of good casting properties, good hot working properties, good cold working properties, good machining properties, good dezincification properties and also be less costly to produce than other low lead alloys so far developed. In particular, the resultant alloys had:

-   -   hot working properties similar to the dezincification resistant         leaded alloy normally used. This was evaluated by comparing both         alloys using the same forging machine and choosing a product         that was considered difficult to manufacture.     -   machining properties that allowed components to be machined with         standard tooling in near standard times when compared to         standard dezincification resistant leaded alloy. This was         evaluated over several production runs of both the standard         leaded alloy and this alloy using standard CNC automatic         equipment.     -   excellent cold working properties when compared to other         dezincification resistant leaded alloy. This was evaluated over         a representative large volume run where considerable cold work         is required at the assembly stage. The number of rejects due to         cracking was much less than is usually experienced when using         the standard leaded dezincification resistant alloy.     -   good casting properties. This was evaluated over a         representative large volume run when it was found that the         casting temperature range and general casting properties were         good to very good.     -   excellent dezincification resistance when tested in a         laboratory. The laboratory test results showed that this alloy         not only had very good resistance to dezincification but also         had very little of the unwanted beta phase present after normal         heat treatment. 

The claims defining the invention are as follows:
 1. A brass alloy comprising: (a) bismuth in an amount in the range from 0.5-1% by weight, (b) lead present in an amount in the range of 0.15-0.25% by, (c) tin present in an amount in the range of 0.25-1% by weight, (d) a dezincification agent(s) present in a total amount in the range of 0.02-0.4% by weight, (e) copper present in the range of 60-63% by weight, and (f) the remainder of the composition being essentially zinc.
 2. A brass alloy according to claim 1 wherein the amount of bismuth is about 0.7% by weight.
 3. A brass alloy according to claim 1 wherein the amount of lead is about 0.22% by weight.
 4. A brass alloy according to claim 1 wherein the amount of tin is about 0.3% by weight.
 5. A brass alloy according to claim 1 wherein the dezincification agent(s) is/are selected from arsenic, phosphorous, antimony and/or any other dezincification agent.
 6. A brass alloy according to claim 5 wherein the dezincification agent(s) is/are present in an amount of 0.02-0.3% by weight.
 7. A brass alloy according to claim 5 wherein the dezincification agent(s) is/are present in an amount of 0.05-0.4% by weight.
 8. A brass alloy according to claim 5 wherein the dezincification agent(s) is/are present in an amount of 0.05-0.2% by weight.
 9. A brass alloy according to claim 5 wherein the dezincification agent(s) is/are present in an amount of about 0.12% by weight.
 10. A brass alloy according to claim 5 where the dezincification agent is arsenic and/or phosphorus.
 11. A brass alloy according to claim 1 further comprising one or more other elements and no individual other element being present in more than 0.2% by weight. 